A question about (Solving a tax rate or interest rate problem using a system of linear equations)
Last year, Shen had $20,000
to invest. He invested some of it in an account that paid 9%
simple interest per year, and he invested the rest in an account that paid 7%
simple interest per year. After one year, he received a total of $1780
in interest. How much did he invest in each account?